Atomic Layer Deposition of Tin Monosulfide Using Vapor from Liquid Bis(N,N′-diisopropylformamidinato)tin(II) and H₂S

Abstract

The oxide and sulfide of divalent tin show considerable promise for sustainable thin-film optoelectronics, as transparent conducting and light absorbing p-type layers, respectively. Chemical vapor deposition (CVD) and atomic layer deposition (ALD) provide attractive routes to these layers. The literature on volatile tin(II) compounds used as CVD or ALD precursors shows that new compounds can provide different growth rates, film morphologies, preferred crystallographic orientations, and other material properties. We report here the synthesis and characterization of a new liquid tin(II) precursor, bis(N, N′-diisopropylformamidinato)tin(II) (1), which is effective in ALD of SnS in combination with H2S between 65 and 180 °C. Like other highly reactive tin(II) precursors, the growth per cycle linearly decreases from 0.82 Å/cycle at 65 °C to 0.4 Å/cycle at 180 °C. This is obviously different from the case of previously reported SnS ALD using bis(2,4pentanedionato)tin(II), Sn(acac)2, and H2S; films grow at 0.22-0.24 Å/cycle almost independent of the substrate temperature (125-225 °C, J. Phys. Chem. C 2010, 114, 17597). Quartz crystal microbalance (QCM) experiments for SnS ALD using 1 at 80, 120, and 160 °C were carried out to study the linear decrease of the growth per cycle with increasing substrate temperature. Based on these QCM studies, although the mechanism of chemisorption-loss of one ligand or two-can be manipulated by changing the exposure of 1, the purging time, or the temperature, only the temperature changes the growth per cycle. We therefore attribute the decreasing growth per cycle with increasing temperature to a decreasing surface thiol density. Photovoltaic devices prepared from 1-derived SnS have similar performance to the best devices prepared from other precursors, and the device yield and replicability of J-V properties are substantially increased by using 1.

Synthesis, Characterization, and Thermal Study of Divalent Germanium, Tin, and Lead Triazenides as Potential Vapor Deposition Precursors

“…However, the deposited GeS was X-ray amorphous, while the GeSe films contained unwanted carbon impurities. SnS has been demonstrated by ALD using the dicoordinated cyclic diamide and, tetracoordinated Sn­(II) formamidinate and amidinate precursors. , The amidinate ligand system provides tetracoordinated, thermally stable, and volatile precursors that afford stochiometric SnS with low levels of impurities.…”

Synthesis, Characterization and Thermal Study of Divalent Germanium, Tin and Lead Triazenides for Atomic Layer Deposition

“…SnS have been demonstrated by ALD using the dicoordinated cyclic diamide 24 and tetracoordinated Sn(II) formamidinate and amidinate. 27,28 The amidinate ligand system provides a tetracoordinated, thermally stable and volatile precursors that afford high-quality…”

“…Compound 2 is only slightly less volatile than Sn(II) formamidinate. 28 This is noteworthy as the formamidinate is the most volatile tetracoordinated M-N bonded Sn(II) literature compound. °C and reduced pressure (~50%).…”

Synthesis, Characterization and Thermal Study of Divalent Germanium, Tin and Lead Triazenides for Atomic Layer Deposition

“…SnS have been demonstrated by ALD using the dicoordinated cyclic diamide 24 and tetracoordinated Sn(II) formamidinate and amidinate. 27,28 The amidinate ligand system provides a tetracoordinated, thermally stable and volatile precursors that afford high-quality SnS films with low levels of impurities. More recently, the first example of ALD grown PbS 29 using Pb-N bonded dicoordinated hexamethyldisilazide 25,30 and cyclic diamide 31 precursors.…”

“…Compound 2 is only slightly less volatile than Sn(II) formamidinate. 28 This is noteworthy as the formamidinate is the most volatile tetracoordinated M-N bonded Sn(II) literature compound. Disregarding the first exotherm for compound 3, the onsets of decomposition for 1-3 from DSC are well above their onset of volatilization.…”